This blog has been posted also in the SAP S/4HANA space. This happened on purpose and we will harmonize and consolidate thecontent in the future as SCN will be renewed - details in Future of SCN - Another Update #1DXCOMMDEST
What are the S/4HANA capabilities to support customer and partner extensions, customization and modifications?
In general with S/4HANA, SAP suggests to differentiate between in-app and side-by-side (ex-app) extensions. This SAP white paper provides insights and guidance:
"Extensibility covers a broad spectrum of topics that allows customers and partners to adapt standard business software to their business needs. It ranges from business configuration; layout adaptation of user interface (UI), forms, and reports; custom fields and logic; integration; and custom terminology and translation to customer-specific applications. Extensibility in theSAP® S/4HANA can be categorized into two main parts: side-by-side extensibility through SAP HANA® Cloud Platform, and in-app extensibility through built-in capabilities"
Obviously the focus for the cloud edition is on ex-app extensibility to maximize SaaS capabilities, whereas for the on premise edition SAP continues to offer all traditional modification, custom coding (z-nnn) and customization capabilities as well.
For more details on HCP - HANA Cloud Platform extension capabilities, please see this link IoT Internet of Things and S/4HANA how HCP can support for example new IoT Internet of Things capabilities while we can maintain high-cadence innovations cycles for S/4HANA.
We will update this space as more details will be be made public.
For more background and different view points, please see also these discussions/pages
Will HCP HANA Cloud Platform be mandatory to customize S/4HANA? in S/4HANA - SAP Business Suite 4 SAP HANA overview
Overview of SAP S/4HANA Cloud options
Mastering SAP Technologies 2015 Melbourne and especially the corresponding comment section (over 100 comments and counting), where for example Bjoern Goerke;provides additional information.